Note: Descriptions are shown in the official language in which they were submitted.
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CA 02218l63 lss7-l0-l4
W096/33045 PCT/SE96/00494
Grinding cup and wear part with vibration dampening means
Techn;c~l f;el~
The present invention relates to a grinding
cup for grinding of cutting inserts of a rock drill
bit, said grinding cup comprising a shank rotatably
mounted in a grinding machine and a wear part being
provided with a recess effectuating the grinding of the
cutting inserts. The invention also relates to a wear
part for the grinding cup.
Pr;or ~rt
During grinding of cemented carbide cutting
inserts of a drill bit, a grinding cup of the above-
captioned type is often used. The wear part of such agrinding cup usually has an abrasive grinding surface
which often comprises di~m~ particles. A grinding cup
for a h~n~h~ld insert grinding machine is known through
SE-B-469 970. The grinding cup is provided with a
specially designed rubber bushing, which has been
mounted to the shank of the grinding cup. The function
of the bushing is to decrease the transfer of
vibrations from the grinding cup to the h~n~held holder
body of the grinding cup. The bushing is however,
mechanically unprotected, such that the bushing may be
subjected to mechanical and abrasive loads.
Sl~m~ry of the ;nvent~on
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An object of the present invention is to
provide a grinding cup that reduces transfer of
vibrations from the grinding cup to the grinding
spindle in connection with grinding of drill bit
cutting inserts by avoiding entrance of abrasive
material to the active contact surfaces. Other objects
of the present invention is to provide a grinding cup
that has a good stability and a good length of life.
The above-mentioned objects have been achieved by
providing a grinding cup that is characterized by the
features of the appended claims.
Descr;pt;on of the figures
Below embodiments of a grinding cup according
to the present invention will be described with
reference to the appended drawings wherein, Fig. 1
shows a side view of a grinding cup according to the
present invention; Fig. 2 shows a side view of an
alternative embodiment of a grinding cup according to
the present invention; Fig. 3 shows a side view of
still another alternative embodiment of a grinding cup
according to the present invention; Fig. ~ shows still
another alternative embodiment o~ a grinding cup
according to the present invention, in a partly
sectioned side view, and Fig. 5 shows cross-section of
an exchangeable wear part according to the present
invention, according to the line V-V in Fig. 4.
Detailed descri~tion of the invention
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The grinding cup 10 according to Fig. 1
~ comprises a shank 11, a wear part 12 and an
intermediate portion 13 connecting the shank 11 with
the wear part 12. Preferably the shank 11 and the
intermediate portion 13 are made in one piece. The
intermediate portion consists of a number of connected
components, see below. The grinding cup 10 is
rotationally symmetric relative to its longitudinal
center axis 14.
The free end of the wear part 12 has a recess
15 in the shape of a spherical segment, when the
cutting inserts 16 to be ground have semi-spherical
free ends. The cutting insert is preferably made of
cemented carbide. If the cutting insert however, has
ballistic, conical or other shape on its free end, the
recess will of course have a corresponding shape. The
recess 15 is adapted to be in engagement and cooperate
with the free end of a cutting insert to be ground. The
wear part is made of sintered powder and at least the
recess is being provided with an abrasive material,
preferably diamond. The other parts of the grinding cup
is preferably made from steel.
The intermediate portion 13 of the grinding
cups 10 can be provided with a key grip at its upper
portion provided to cooperate with a driving means of
the grinding machine to rotate the grinding cup 10. A
central flush channel 18 extending axially, extends
between the free end of the shank 11 and a central
and/or eccentric orifice in the recess 15. The shank 11
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and the intermediate portion 13 may alternately be
provided with other conventional geometry's, suited for
different kinds of grinding machines available on the
market.
The radially outermost border line of the
recess 15 has a diameter D. Radially outside the
outermost border line, the wear part is provided with a
backed-off conical surface 19 or a circular surface
perpendicular to the center axis 14. Said surface 19
connects to the jacket surface 20 of the wear part over
an obtuse 21 or perpendicular corner. The jacket
surface connects to a first part 17 of the intermediate
portion 13, either continuously or via a transition
such as a corner 22. The part 17 has an outer diameter
which may be larger than but preferably equal to or
less than the diameter of the jacket surface. The first
part is preferably made integral with the wear part.
The wear part 12 may alternately be bonded to the first
part 17 in another manner, preferably by brazing. The
~irst part 17 is firmly connected via a first joint 24
to a second part 23 by gluing or vulcanization. The
second part 23 consists of a flexible, vibration
dampening material, such as rubber for example. The
second part is furthermore connected to a third part 25
of the portion 13, which in turn is connected to the
shank 11. The third part 25 is firmly connected via a
first joint 26 to the second part 23 by gluing or
vulcanization. The center hole of the second part has a
diameter that preferably is larger than the diameter of
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the flush channel 18 to avoid decrease in flow. The
joint surfaces 24 and 26 are preferably plane parallel
and perpendicular to the center axis 14 of the grinding
cup. Alternately the joint surfaces may be curved. The
flush channel 18 extends centrally through the parts
17, 24 and 25. The diameters of the latter parts are
substantially equal and preferably larger than the
diameter D of the recess, said grinding cup obtaining a
relatively good stability, via guiding radially close
to the jacket surface or in the jacket surface,
simultaneously as transfer o~ the vibrations is
prevented.
The described grinding cup 10 functions as
follows. The grinding cup iû is mounted ln the
rotatable spindle of a grinding machine. The grinding
cup is thereafter adjusted in position relative to the
cutting insert to be ground, i.e. in a position where
the wear part 12 is in contact with the cutting insert.
The grinding cup 10 is then rotated to perform grinding
of the cutting insert.
Flushing medium is supplied from an outer
source to the recess 15 via the flush channel 18.
Substantially all flushing medium shall be supplied to
the active surface of the cutting insert. Driving of
the wear part 12 is done via the second part 23, which
is flexible in both the tangential and axial directions
and the vibrations that arise will be leveled in the
part 23.
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In Fig. 2 is shown an alternative embodiment
o~ a grinding cup 10' according to the present
invention. The only thing that dif~ers ~rom the
embodiment according to Fig. 1 is that the second part
5 17 o~ the intermediate portion 13 has been expelled and
thus that the second part 23 ' has been joined directly
to the wear part 12 ' via the joint sur~ace 24 ' . The
third part 25 ' is thus a larger piece o~ the part 13 '
compared to the embodiment according to Fig. 1.
Otherwise the information given in connection with Fig.
1 is true also for this embodiment.
In Fig. 3 is shown still another alternative
embodiment of a grinding cup 10" according to the
present invention. The only thing that di~ers ~rom the
15 embodiment according to Fig. 1 is primarily that the
third part 25 " o~ the intermediate portion 13 " has the
shape o~ a socket. The socket has a central cylindrical
cavity 2 7 ", which is provided to receive a ~lexible
second part 23 " in its entirety and partly the ~irst
part 17". The second part 23" is vulcanized or glued to
the socket and to the ~irst part via joint sur~aces 24 "
and 26". The joint sur~aces are pre~erably plane
parallel and perpendicular to the center axis o~ the
grinding cup. A gap 28 " iS provided in the radial
25 direction between the second part 23 " and the
cylindrical wall o~ the cavity 27", in order to create
a space ~or expansion ~or the part 23 " ~ which is needed
when the grinding cup 10" is subjected to axial load.
An advantage with this alternative embodiment is that
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the part 17" can be guided by the cyllndrical inside of
the socket at angled loads on the wear part 12".
The three embodiments 10-10" described above
provide the advantage that the grinding cup reduces
transfer of vibrations from the grinding cup to the
grinding spindle in connection with grinding of drill
bit cutting inserts in combination with a simple
handling and a good length of life.
In Figs. 4 and 5 is shown still another
alternative embodiment of a grinding cup 10'''
according to the present invention, partly in cross-
section. The shank 11''' has an external thread at its
free end, which in a threaded connection 29'''
cooperates with an internal thread of the intermediate
portion 13''' of the third part 25'''. The part 25'''
has an internal cavity 27''' which consists of at least
two substantially cylindrical surfaces, an upper
surface 30''' of which has a larger diameter than a
lower surface 31'''. The threaded connection provided
to tightened in working direction of the machine. The
second part 23''' consists of a flexible means which
dismountably abuts against the wear part and the shank
via contact surfaces 24''' and 26''', respectively. A
radial gap 28''' is provided between the part 23''' and
the upper surface 30''', in order to create a space for
expansion for the part 23''', which is needed during
~ axial loading of the grinding cup 10'~. The wear part
is partly received by the lower surface 31''' and in a
central hole 32''' connected to the latter surface. A
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collar 33''' is provided between the hole and the lower
sur~ace. The collar cooperates with a peripheral
shoulder 34''' on the wear part, ~acing towards the
recess 15''', to ~orm an axially ~orward stop. A groove
35''' is provided in the shoulder to receive a driving
pin 36''', axially secured in the part 25'''.
The described grinding cup 10''' is mounted as
~ollows. The wear part 12''' is placed in the part
25''' such that the pin enters the groove 35'''
wherea~ter the wear part is pushed down, such that the
shoulder and the collar mutually engage. Then the means
23''' is placed in position to abutment against a rear
side o~ the wear part, the largest diameter o~ said
means pre~erably being less than the smallest diameter
o~ the threaded portion o~ the part 25'''. Then the
threaded connection 29''' is tightened until the part
23''' has been compressed to a desired degree. An
advantage with this alternative embodiment is that the
wear part 12''' may be exchanged separately, such that
the same shank may be used ~or grinding di~erent
shapes o~ cutting inserts. Furthermore, the rigidity
and the neutral frequency o~ the grinding cup can be
ad~usted depending on mach;n~ng conditions.
The present invention thus relates to a
grinding cup where the wear part is resilient in the
grinding cup in at least the axial direction relative
to the shank and where the resilient means ~orms
contact sur~aces with connecting parts, said contact
sur~aces having substantially the same radial
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extension. By that the grinding cup will achieve a good
length of life by avoiding entrance of abrasive
material to the contact surfaces. The means 23-23'''
preferably seals between the shank and the wear part
such that the flow of flushing medium is maintained. It
is understood that the flush channel in the wear part
may be centrally or eccentrically placed.
